linux-kernel - Re: [PATCH 3/8] net: qualcomm: rmnet: use field masks instead of C bit-fields

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Date:   Mon, 20 May 2019 08:43:36 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Alex Elder <elder@...aro.org>
Cc:     arnd@...db.de, subashab@...eaurora.org, david.brown@...aro.org,
        agross@...nel.org, davem@...emloft.net,
        ilias.apalodimas@...aro.org, cpratapa@...eaurora.org,
        syadagir@...eaurora.org, evgreen@...omium.org, benchan@...gle.com,
        ejcaruso@...gle.com, netdev@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/8] net: qualcomm: rmnet: use field masks instead of C
 bit-fields

On Mon 20 May 06:53 PDT 2019, Alex Elder wrote:

> Using C bitfields (e.g. int foo : 3) is not portable.  So stop
> using them for the command/data flag and the pad length fields in
> the rmnet_map structure.  Instead, use the functions defined in
> <linux/bitfield.h> along with field mask constants to extract or
> assign values within an integral structure member of a known size.
> 

Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>

> Signed-off-by: Alex Elder <elder@...aro.org>
> ---
>  drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c | 5 +++--
>  drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h      | 8 +++++---
>  drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c | 5 ++++-
>  3 files changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> index 4c1b62b72504..5fff6c78ecd5 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> @@ -13,6 +13,7 @@
>   *
>   */
>  
> +#include <linux/bitfield.h>
>  #include <linux/netdevice.h>
>  #include <linux/netdev_features.h>
>  #include <linux/if_arp.h>
> @@ -70,7 +71,7 @@ __rmnet_map_ingress_handler(struct sk_buff *skb,
>  	u16 len, pad;
>  	u8 mux_id;
>  
> -	if (map_header->cd_bit) {
> +	if (u8_get_bits(map_header->cmd_pad_len, RMNET_MAP_CMD_FMASK)) {
>  		if (port->data_format & RMNET_FLAGS_INGRESS_MAP_COMMANDS)
>  			return rmnet_map_command(skb, port);
>  
> @@ -78,7 +79,7 @@ __rmnet_map_ingress_handler(struct sk_buff *skb,
>  	}
>  
>  	mux_id = map_header->mux_id;
> -	pad = map_header->pad_len;
> +	pad = u8_get_bits(map_header->cmd_pad_len, RMNET_MAP_PAD_LEN_FMASK);
>  	len = ntohs(map_header->pkt_len) - pad;
>  
>  	if (mux_id >= RMNET_MAX_LOGICAL_EP)
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> index a30a7b405a11..a56209645c81 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> @@ -40,13 +40,15 @@ enum rmnet_map_commands {
>  };
>  
>  struct rmnet_map_header {
> -	u8  cd_bit:1;
> -	u8  reserved_bit:1;
> -	u8  pad_len:6;
> +	u8  cmd_pad_len;	/* RMNET_MAP_* */
>  	u8  mux_id;
>  	__be16 pkt_len;
>  }  __aligned(1);
>  
> +#define RMNET_MAP_CMD_FMASK		GENMASK(0, 0)   /* 0: data; 1: cmd */
> +#define RMNET_MAP_RESERVED_FMASK	GENMASK(1, 1)
> +#define RMNET_MAP_PAD_LEN_FMASK		GENMASK(7, 2)
> +
>  struct rmnet_map_dl_csum_trailer {
>  	u8  reserved1;
>  	u8  valid:1;
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> index 498f20ba1826..10d2d582a9ce 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> @@ -13,6 +13,7 @@
>   *
>   */
>  
> +#include <linux/bitfield.h>
>  #include <linux/netdevice.h>
>  #include <linux/ip.h>
>  #include <linux/ipv6.h>
> @@ -301,7 +302,9 @@ struct rmnet_map_header *rmnet_map_add_map_header(struct sk_buff *skb,
>  
>  done:
>  	map_header->pkt_len = htons(map_datalen + padding);
> -	map_header->pad_len = padding & 0x3F;
> +	/* This is a data packet, so cmd field is 0 */
> +	map_header->cmd_pad_len =
> +			u8_encode_bits(padding, RMNET_MAP_PAD_LEN_FMASK);
>  
>  	return map_header;
>  }
> -- 
> 2.20.1
>